The general goal of these studies is to gain an understanding of the conduction and gating of ionic currents through voltage sensitive sodium channels. To approach this goal, I will perform experiments on channels from mammalian brain incorporated into planar lipid bilayers as well as on voltage-clamped squid giant axons. Traditional bilayers formed between two aqueous chambers will be used when large membrane areas and easy access to solutions on both sides of the membrane are required. Micron-dimensioned bilayers formed on pipet tips, will enable the highest resolution of current records from single channels. The effects of incorporation into the artificial bilayers will be examined by comparing properties of incorporated channels with those observed by patch-clamping native membrane vesicles. Surprisingly, in initial studies of incorporated, batrachotoxin (BTX)-activated channels showed selectively near that of normal nerve. Hence, I plan a detailed evaluation of conduction in single BTX-treated channel, and subsequent studies in the absence of any activating alkaloid. I will take advantage of the ability offered by the bilayer system to separately manipulate fixed charges on the channel protein and the surrounding lipid. An attempt will be made to map the location of charges that affect either gating, ion permeation, or channel block by impermeant ions or toxins. Studies in squid axon have shown that addition of nonelectrolytes to the aqueous phase slows kinetics of gating and channel block, and reduces conductance. The mechanism of these changes will be investigated at the single channel level using the channels inserted into bilayers. Throughout this work, an underlying goal will be ultimately to develop the ability to measure single- and multi-channel ionic currents and gating currents in the same preparation. Experiments on squid axon will determine whether saxitoxin block of BTX-activated channels is voltage-dependent, as it is for brain channels in bilayers, as well as allow further comparison of native and incorporated channels.